1. Field of the Invention
The present invention relates to an improved tappet assembly interposed between an overhead cam shaft and the stem of a standard poppet valve of an internal combustion engine. The effective thickness of such tappet assembly is adjustable to eliminate valve lash without requiring disassembly of the engine.
2. Prior Art
In a conventional overhead cam internal combustion engine, a composite tappet assembly commonly includes an inverted cup follower fitted in a cylindrical bore of the cylinder head in line with the upward-projecting stem of each intake and exhaust valve. Shims can be used to achieve a desired clearance between the top of the valve stem and the follower. The top of the follower is engaged by a lobe of the cam shaft. Ideally, the clearance is set and periodically adjusted so that valve lash is eliminated, i.e., the clearance is zero when the engine reaches its normal operating temperature. It can be timeconsuming, painstaking work to set or adjust the clearance by use of shims.
The construction shown in my earlier U.S. Pat. No. 3,675,631, issued July 11, 1972, is representative of prior attempts to provide adjustable tappet assemblies that eliminate the need for separate shims. In the construction shown in that patent, the inverted cup follower has a threaded central bore receiving a complementally threaded plug for engaging against the top of the valve stem. The top of the plug has a square socket receiving a square tongue of a cap member. Turning the cap member rotates the plug to advance it toward the valve stem or to retract it away from the valve stem.
In my previous construction, the cup follower has a series of "locking holes" concentric with its central bore, and the cap member has a downward-projecting pin normally received in one of such holes so as to prevent rotation of the cap and the plug relative to the cup. In order to adjust the valve clearance, the cap must be wedged upward to free its downward-projecting pin from the locking hole, whereupon the cap can be turned to rotate the plug. When the desired position has been achieved, the cap is lowered for reception of the downward-projecting locking pin into one of the locking holes.
Other known constructions which use relatively rotatable threaded members for adjusting the valve clearance are shown in the following U.S. patents:
U.S. Pat. No. 1,496,497, issued June 3, 1924 (Swarthout et al.);
U.S. Pat. No. 3,002,508, issued Oct. 3, 1961 (Barker et al.);
U.S. Pat. No. 3,301,239, issued Jan. 31, 1967 (Thauer);
U.S. Pat. No. 3,413,964, issued Dec. 3, 1968 (Pask);
U.S. Pat. No. 3,941,102, issued Mar. 2, 1976 (Barham);
U.S. Pat. No. 4,321,894, issued Mar. 30, 1982 (Black).